Converting Digital Zoom to 35mm Equivalent

[Nizidramanii]

I've seen many of you do this before. How do you do it? There does not seem to be a direct conversion factor. I'm guessing that there is an offset of some kind.

[JimC]

If you want to see how the angle of view compares, you simply multiply the 35mm equivalent focal length by the amount of Digital Zoom.

For example, KM says this about their DiMAGE Z6 in some of the marketing material:

Incredible 48x Total Zoom Range - Combining the built-in 12x optical zoom lens with the 4x digital zoom gives photographers a total zoom range of 48x, ideal for taking shots over long distances at sporting events or when capturing distant landscapes. This incredible optical zoom lens delivers a focal range equivalent to a 35mm - 420mm lens on a 35mm camera lens. With the digital zoom, the total zoom range is equivalent to 35mm - 1,680mm on a 35mm camera.

So, all they did was multiply the420mm equivalent focal lengthby the "4x Digital Zoom" to get 1680mm (4 x 420mm = 1680mm). But, all that means is that you'll have the same angle of view as a lens that long on a 35mm camera. Of course, the 48x part is also misleading. All that kind of thing means is that the longest focal length is that many times the shortest focal length (and in the case of Digital Zoom withmost models, it's done by cropping and enlarging).

Keep in mind that you candegrade quality when you use Digital Zoom. You're not adding any detail by using it (and you can degrade detail if the interpolation algorithms in the camera aren't good enough for resizing back up to the original resolution after the cropping, since the algorithms are adding pixels that were not captured by the sensor).

I make sure Digital Zoom is disabled on any cameras I use withit (just to make sure I don't accidently use it). But, some users seem to like it (even though you can just crop and enlarge again using software later if needed with more time for the exact composition you're looking for).

Of course, cropping with software doesn't help with the number of pixels representing your subject either, and the quality of the resizing algorithms you usecan impact final results (if you need to interpolate to have enough pixel density for the desired print size).

Basically, there is no substitute for Optical Zoom if you need to bring your subject in closer, and you'll need to take the print size and subject type into consideration before cropping too much, to make sure you have enough pixels representing the detail desired in your subject for the desired print size (and the same applies for Digital Zoom).

[Nizidramanii]

OOPS! I guess I didn't phrase my title correctly. I really meant, "Converting Digital Camera Zoom to 35mm Equivalent"

Just plain zoom, not digital zoom alone.

For example, the Canon S2 IS has an optical zoom of 12x, which converts to 432mm. How do you convert 12x to 432? I've played around a bit and I think you multiply the 12x by 36 to get 432, but it doesn't seem to work out perfectly in all cases.

[JimC]

Nizidramanii wrote:

I've played around a bit and I think you multiply the 12x by 36 to get 432, but it doesn't seem to work out perfectly in all cases.

That's exactly what they're doing. All the 12x means is that the longest focal length is 12 times the shortest focal length. It may not be "exact" in all cases. but the manufacturers are just trying to make it sound as good as possible.

Ignore this number. It has nothing to do with your angle of view/apparent magnification. It's just a number to make a camera sound better that the marketing people are using. All it's really telling you is how much difference there is between the widestzoom setting, and the longest zoom setting.

For example, a lens with a 35mm equivalent focal range of 24-240mm could be called a 10x zoom; and a lens with a focal range of 50-500mm could also be called a 10x zoom (even though it's more than twice as long as the shorter zoom).

[Nizidramanii]

Thanks Jim! That was the little puzzle piece that I was looking for. That would explain why the 36 factor doesn't apply to cameras with 35 or 28 mm wide angle.

Now I realize that a camera with a 28mm wide angle and a 4x zoom will not zoom in as far as a camera with a 4x zoom and 35mm wide angle. That helps a lot